Electron Beam Of Duration Research Articles

Limitation of runaway electron beam duration in air-filled gap with inhomogeneous field

Alternative factors that account for a limitation of the period of injection of picosecond runaway electron bunches in air-filled diode with inhomogeneous electric field are analyzed. Experimental data on the characteristics of such electron beams have been obtained under the conditions with variable emissive properties of the cathode, time of the voltage prepulse action, and electric field strength in the region of electron injection. Based on these data, a hypothesis is formulated and justified that the mechanism of limitation related to a transition from the field electron emission to the explosion of microinhomogeneities is less probable than the mechanism of current limitation by a screening plasma cloud formed over the point electron emitters.

Detonation of PETN single crystals initiated by an electron beam

Luminescence in the volume of PETN (tetranitropentaerytrite) single crystals exposed to an electron beam (duration 20 nsec) with an energy density of 15 J/cm2, which exceeds the threshold of explosive decomposition, was investigated in real time. Exposure to the ionizing pulse causes radioluminescence and emission related to the critical electron emission from a dielectric which is transformed to a vacuum discharge. The emission zone propagates from the surface into the vacuum at a speed of 5000–6500 m/sec. The absorption of electron beam energy in the irradiated layer (0.25 mm) causes the formation and propagation of a shock wave enhanced by the chemical reaction in the crystal. When the shock wave is reflected from the target on the rear side of the sample, its amplitude increases. This leads to detonation accompanied by emission which propagates from the backside to the irradiated surface of the sample at a speed of 7500–8500 m/sec with the subsequent expansion of the explosive decomposition products into the vacuum.

Quasimonoenergetic Electron Beams with Relativistic Energies and Ultrashort Duration from Laser-Solid Interactions at 0.5 kHz

We investigate the production of electron beams from the interaction of relativistically-intense laser pulses with a solid-density SiO(2) target in a regime where the laser pulse energy is approximately mJ and the repetition rate approximately kHz. The electron beam spatial distribution and spectrum were investigated as a function of the plasma scale length, which was varied by deliberately introducing a moderate-intensity prepulse. At the optimum scale length of lambda/2, the electrons are emitted in a collimated beam having a quasimonoenergetic distribution that peaked at approximately 0.8 MeV. A highly reproducible structure in the spatial distribution exhibits an evacuation of electrons along the laser specular direction and suggests that the electron beam duration is comparable to that of the laser pulse. Particle-in-cell simulations which are in good agreement with the experimental results offer insights on the acceleration mechanism by the laser field.

Evaluation of the experimental parameters which control electron detachment dissociation, and their effect on the fragmentation efficiency of glycosaminoglycan carbohydrates

The efficiency of conversion of precursor ions to observable products for electron detachment dissociation (EDD) was measured as a function of the key experimental parameters to determine their optimal values for the Fourier transform mass spectrometry analysis of anionic glycosaminoglycan carbohydrates. These parameters include electron current, electron energy, dispenser cathode heater current, electron beam duration, charge state of the precursor ion, oligomer length, and precursor ion number accumulated in an external radio frequency multipole trap. Precursor conversion is most efficient at an electron current of 15 μA, and decreases at higher and lower values. The conversion of precursor to product ions increases in efficiency as the electron pulse duration is increased. Together, these data suggest that a radially repulsive electric field is produced between the electron beam and negative ions during EDD which causes the reaction cross-section to decrease at higher values of electron current (>15 μA). Elevating the heater current of the dispenser cathode increases the electron flux, but also causes ion activation, presumably by blackbody infrared irradiation. An electronic circuit is described that allows the electron current produced by the dispenser cathode to be measured during an EDD or electron capture dissociation (ECD) experiment.

Repetitively pulsed CO2 laser driven by an electron accelerator with a gas-discharge plasma cathode

A repetitively pulsed electron-beam-controlled CO2 laser driven by an electron accelerator with a plasma electron emitter based on low-pressure glow discharge with hollow anode and cathode is presented. The application of the proposed emitter makes it possible to sharply increase the current and to control the electron-beam duration and, hence, the energy and time characteristics of the laser. It is demonstrated that the radiation pulse duration ranges from 300 to 1200 μs, whereas the radiation energy amounts to 200 J at an efficiency of 18%. In the course of lasing, the focal spot is not affected by the heterogeneous heating of the active medium. A significant heterogeneity in the gas flow upon an incomplete renewal of the gas in the zone filled with radiation leads to an increase in the focal spot owing to the wavefront distortions.

Repetitively pulsed operating regime of a high-pressure atomic xenon transition laser

The repetitively pulsed regime of an atomic xenon transition laser pumped by an electron beam with various pulse durations and an electron-beam-initiated discharge is studied experimentally. An average radiation power of 2.5 W has been achieved in a quasi-stationary regime for a pulse repetition rate of 5 Hz in a laser pumped by a radially convergent electron beam of duration 100 μs without circulation of the Ar — Xe working mixture. The average output power for a laser pumped by a planar electron beam in quasi-stationary regime is 2 W. It is shown that for a specific energy contribution not exceeding 50 J L-1 and laser excitation by a train of electron-beam pulses at a repetition rate of 50 Hz, the amplitude and duration of the second lasing pulse virtually coincide with those of the first. For a laser pumped by a discharge initiated by a nanosecond electron beam, an average lasing power of 380 mW is achieved under steady-state conditions upon transverse circulation of the working mixture and a pump pulse repetition rate of 25 Hz. Pumping by an electron beam from two accelerators with a pulse duration of a few tens of microseconds under an Ar — Xe mixture pressure of about 1 atm and a specific pump power of 1 — 3 kW cm-3 per pulse is proposed for the development of 1.73-μm repetitively pulsed Xe lasers with a high average output power.

Pulsed electron-beam treatment of WC–TiC–Co hard-alloy cutting tools: wear resistance and microstructural evolution

The mechanisms for changes in the structure-phase state, microhardness, and wear resistance have been investigated for carbide inserts made of type T15K6 (WC–15TiC–6Co) hard alloy, irradiated with a low-energy (20–30keV, high-current (∼102Acm−2) electron beam of duration 2.5μs. Using transmission electron microscopy, it has been established that the pulsed melting of the near-surface (∼1μm) layer results in the formation of a subgrain structure in the binding phase, segregation of nanosized carbide particles in the near-boundary regions, and the allotropic transformation of WC. The irradiation increases by about three times the durability of the inserts at elevated cutting rates for steels. The increase in durability is associated with the efficient hardening of the Co binder immediately on irradiation and with its high thermal stability being retained in the process of cutting due to the stability of the dislocation substructure provided by second-phase segregates.

Calculation and experimental determination of dimensions of hardening and tempering zones in quenched U7A steel irradiated with a pulsed electron beam

Based on metallographic data and microhardness depth distributions measured in preliminarily quenched and tempered U7A steel11American analogue is W1-07C Extra steel. (0.7% C) after irradiation with an electron beam of duration 10−5 s, electron energy 170–180 keV and energy density 40–150 J/cm2, the dimensions of the hardened and tempered zones have been determined. The experimental results are compared with those obtained by solving numerically the heat equation taking into account the processes of melting, evaporation, and crystallization. Good agreement between experimental and theoretical data is observed.

Investigation of Raman free-electron lasers with a bifilar helical small-period wiggler

A Raman free-electron laser with a novel bifilar helical small-period wiggler is presented. The magnetic characteristics of such a wiggler are measured, and the maximum transverse field of the wiggler as high as 1500 G has been obtained with the wiggler period 10 mm and gap 15 mm. The experimental results indicated that the free-electron laser operates in the range of 3 mm when using a limited pulse duration of electron beam (300 keV/400 A, 50 ns), and the maximum laser power of 600 kW is observed, corresponding to electron efficiency of 0.5%. >

Sublimation and diffusion of arsenic implanted into silicon at rapid electron beam annealing

Properties of silicon layers implanted with As + ions (100 keV, 10 16 cm −2) through 30 nm SiO 2 film and annealed in vacuum by means of a 15 s duration electron beam were studied using Rutherford backscattering plus channeling and electrical measurements. The influence of the irradiation conditions on As activation, diffusion and sublimation, as well as on the crystal structure perfection of the samples are discussed. Results have been obtained which testify to As sublimation and diffusion in connection with its deactivation in the area of realization of an electrically active As nonequilibrium concentration.

Cavity length adjustment and output FEL intensity optimization

The authors reconsider in more quantitative detail the possibility of enhancing the output intensity of a free electron laser (FEL) oscillator operating with bunched electron beam and finite macropulse duration, adjusting the cavity length while the signal grows. In a forthcoming publication G. Dattoli et al. point out that the output power can be enhanced by moving the cavity mirrors while the intercavity signal grows in such a way that the system is operating at the value of the cavity length providing the maximum gain. Practical solutions to realize the mirror movements are also discussed. The authors complete the analysis to be published by presenting simple formulas which allow a straightforward evaluation of the power enhancement.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Control of gigawatt REB pulse duration using gas injection

A technique for controlling the voltage and current pulse duration of a gigawatt relativistic electron beam (REB) was investigated. The pulse duration of a beam of 250 keV and 10 kA was controlled from 60 ns to 10 ns by injecting gases (air,, argon, and hydrogen) into the diode gap at a pressure ranging from 10/sup -5/ torr to 10/sup -1/. The observed dependence of the pulse duration on the nature and pressure of the gas is explained in terms of volume ionization of the gas by beam electrons. It is concluded that the pulse duration is governed by the time at which the plasma density created by the beam reaches a critical value of the order of beam electron number density.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Conductivity of polyethylene terephthalate induced by high electron beam current densities

The radiation induced conductivity (RIC) of polyethylene terephthalate (Mylar) produced by the electron beam from a pinched electron beam diode has been measured experimentally. Data were obtained for 4–10 ns duration electron beam pulses at radiation dose rates up to 4×1016 rad/s (100 kA/cm2 current density). The conductivity is roughly proportional to radiation dose rate up to about 100 Mrad and at higher doses scales approximately with radiation dose to the (3)/(2) power. The experimental data are compared to the predictions of a model of RIC using dispersive electronic transport and bimolecular recombination. The parameters used in the model were obtained from published low dose (&amp;lt;100 rad) time-resolved photoconductivity measurements on Mylar. The data agreed well with the calculations before the onset of significant sample heating (10 Mrad). The highest reported RIC results are compared to the expected results for a weakly ionized plasma experiencing electron neutral collisions. In this case the experimental conductivity is significantly higher than the calculated value.

Quenching kinetics of electron beam pumped XeCl

The rates of several piocesses removing XeCl * subsequent to its formation by short duration electron beam excitation of Ar/Xe/CCl 4 mixtures have been investigated. A dominant third-order reaction with Xe and Ar has been identified. The effective radiative lifetime of XeCl * has been measured as 41±3 ns.

Dominant formation and quenching kinetics of electron beam pumped Xe2Cl

Processes leading to the production and removal of the triatomic excimer Xe2Cl* subsequent to short duration electron beam excitation of Ar/Xe/CCl4 mixtures have been investigated. The radiative lifetime of Xe2Cl* has been measured to be 135 (+70−60) ns. Formation of the excimer has been shown to occur principally via a termolecular reaction involving XeCl*. Rate constants for the formation and collisional quenching of Xe2Cl* by CCl4, Xe, and Ar have been determined.

Efficient XeF laser with discharge stabilized by short-duration electron beam

Experimental and theoretical investigations have been carried out on the efficient operating conditions of an XeF laser with discharge stabilized by an electron beam of duration 50 nsec. The experimental values obtained were ∼0.15 J (∼3 J/liter) for the radiative energy per pulse and ∼1.5% for the efficiency.

Special features of the operation of an electron-ionization CO2-laser at high pressures

A study was made of the excitation of the working medium of a CO2-laser at a pressure of up to 8 atm by an electron beam of duration 15 · 10−9 sec. Results are given of the energy dissipation in a CO2:N2-1∶3 gas medium in the whole range of pressures with E0/p = (18–38) V /cm · mm Hg. The dependences of the time of appearance of the stimulated radiation with respect to the current pulse are given.

The Hydra Electron Beam Generator

The Hydra electron beam generator was designed to simrultaneously produce two 1 MV, 0.5 MA, 80 nanosecond electron beams that could be combined to form a single beam. The machine, undergoing final developmental tests, has generated a 0.5 MA, 1 MV peak electron beam from each line. This accelerator consists of a low-inductance Marx generator, two water-dielectric pulse-forming (PF) and impedance-transforming transmission lines and two low-inductance, high-current diodes. A description of the generator is presented along with developmental studies and initial testing data. The Hydra machine is based on accelerator principles described in the literature. The Marx generator is submerged in transformer oil and separated from the transmission line water by a lucite interface. The Marx charges each coaxial PF transmission line which is deionized water insulated to 3 MV in 0.9 microseconds. At peak voltage, a 3 MV SF6 spark gap electrically connects the 4 ohm PF line to the impedance transforming (4 ohm to 2 ohm) transmission line. The pulse is transmitted through this line to the single radial insulator diode. A 30 kilojoule, 100 nanosecond duration electron beam is formed by a cold cathode in each diode.